1. Field of the Invention
This invention pertains to magnetic recording, and particularly to transducing heads for recording and reproduction of signals on/from magnetic tape.
2. Related Art and Other Considerations
In the time frame from about the year 1955 to about the year 1970, tranducing heads for helical scan tape drives were designed with simple construction. In these simple heads the two magnetic pole halves (which were joined to form a magnetic gap therebetween) were of uniform thickness such that the effective magnetic headwidth, H11, was equal to the physical tape contact width, H21, as shown in FIG. 1.
As recorded track densities increased (circa early 1970s), smaller effective magnetic headwidths were required. In view of the requirement for smaller headwidths, it was not practical for tribological reasons to reduce the physical tape contact width by the same amount. Consequently, manufacturers developed a new design (illustrated in FIG. 2) wherein one of the two magnetic pole pieces was micro-machined to create a smaller effective magnetic headwidth, H12, while providing a larger physical tape contact width, H22. In this regard, see also U.S. Pat. No. 3,813,693 to Gooch et al.
When narrow-track azimuth digital recording formats (e.g., D-2) were developed in the mid-1980s, a construction similar to that of FIG. 3 was successfully used. In FIG. 3, xcex1 represents the azimuth angle. The FIG. 3-tyype structure worked well because the physical tape contact width, H23, was less than the width of three adjacent recorded tracks, 3T3 (i.e. H23 less than 3T3). FIG. 4 illustrates how a read head of FIG. 3 would be positioned relative to the pattern of recorded alternating azimuth tracks each of width T3. As understood from FIG. 4, the desired signal is recovered from Region I where the effective magnetic read headwidth overlaps the desired same-azimuth recorded track, and the undesired signals from Regions II and III are greatly reduced by the well-known azimuth-loss effect since the recorded transitions in these areas are not parallel to the effective magnetic headwidth nor to the edges of the wider magnetic pole half.
Ultra-narrow-track azimuth digital recording formats, such as that involved in the Mammoth(trademark) tape drive technology developed by Exabyte Corporation, were developed in the early-1990s. In this ultra-narrow-track azimuth digital recording format, a read head design similar to that of FIG. 3 was no longer useful, since again for tribological reasons, the physical tape contact width, H25, could not be made less than the width of three adjacent recorded tracks. Consequently, the physical tape contact width, H25, would now overlap 5 or more adjacent tracks as shown in FIG. 5. Since the edges of the wider magnetic pole half now overlapped adjacent tracks where the transitions are parallel to these edges, the undesired signals picked up from these areas (Regions IV and V) are not reduced by the azimuth-loss effect and the SNR of the system suffers greatly.
To overcome the problems described above, manufacturers developed another new head type where both of the magnetic pole halves are micro-machined as shown in FIG. 6. While the construction of FIG. 6 eliminates the undesired signal pick-up from Regions IV and V, it has some disadvantages compared to the design of FIG. 3. A first such disadvantage is that the magnetic efficiency of the head is reduced since the cross-sectional area of the magnetic material near the magnetic gap area is reduced. A second disadvantage is that the design requires micro-machining both of the magnetic pole halves. A third disadvantage is that alignment of the two magnetic pole halves relative to each other is criticalxe2x80x94any misalignment between the magnetic pole halves reduces the effective magnetic headwidth, H1.
What is needed, therefore, and an object of the present invention, is a transducing head that has higher magnetic efficiency and improved manufacturability compared to the conventional ultra-narrow track read head design.
A transducing head for a magnetic tape recorder comprises a first magnetic pole and a second magnetic pole positioned to form a gap therebetween. The first magnetic pole has a first magnetic pole width H3 along the gap and the second magnetic pole has a second magnetic pole width H1 along the gap. The first magnetic pole width H3 and the second magnetic pole width H1 are formed to satisfy the relation H1 less than H3 less than 3T less than H2, wherein H2 is a physical tape contact width of the transducing head and 3T is a width of three adjacent recorded tracks traversed by the head.